Recently, adapters have been developed which provide personal computers, in particular portable computers, with the capability to communicate with other computers via a radio telephone network infrastructure.
For the present generation of portable computers, such adapters are typically marketed in the form of data cards configured in accordance with well known Personal Computer Memory Card International Association (PCMCIA) standards. Such data cards contain the logic and software that allow a portable computer to communicate over a radio telephone network infrastructure via a mobile telephone, such as a Global System for Mobile Communications (GSM) mobile telephone. The existing facilities of the mobile telephone are used to allow data communication via the radio telephone network, with the mobile telephone supporting the various protocols required for communication over the network.
Similar devices have also been proposed, known as transceivers, which are in the form of PCMCIA data cards but which themselves contain all the hardware and software functions of a mobile telephone, so that a separate mobile telephone is not required.
Generally, the design of known such data cards of both types is such that the card appears to the computer to be a conventional wired modem. In other words, the computer communicates via the card through one of the serial communications (COM) ports of the computer using exactly the same interfaces and commands that it would use with a wired modem. The advantage of this approach is that existing software, which has been developed for use with conventional wired modems can be used unchanged with the data cards.
However, modern digital radio telephone networks offer more facilities than the traditional analog telephone networks for which conventional modems were designed. Consequently, there are differences between a conventional modem and a data card which is designed, for instance, for use with a GSM network. A GSM data card, for example may offer not only data transport services, but may also be able to make use of supplementary services offered by the network, such as call cost and signal strength indications, and paging or messaging services. In modern networks, such as GSM networks, such additional services can be used concurrently with voice or data communications, so that one can receive a short message over the network whilst at the same time receiving a telephone call.
However, the use of these extra facilities via a conventional data card poses a problem because the architecture of present personal computers does not allow serial COM ports to be shared by simultaneous applications. So, for example, if a user wishes to leave a fax application running which is waiting to receive incoming faxes via the data card, they cannot at the same time read any short messages they receive using another application. In order to receive incoming short messages, the user must end and restart the fax application, which may not be easy or convenient.
Devices are known which allow at least paging services to be exploited by a computer and a data card. For example, U.S. Pat. No. 5,455,572 describes a pager in the form of a computer peripheral device which communicates with a computer via a PCMCIA memory-only interface. However, this device does not at the same time provide a data transport connection to the network via a serial COM port.